Synthesis and characterization of phthalonitrile resins from ortho-linked aromatic and heterocyclic monomers
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This article describes the synthesis and properties of phthalonitrile polymers prepared from three different ortho-linked monomers, namely 2,2′-bis(3,4-dicyanophenoxy)biphenyl, 1,2-bis(3,4-dicyanophenoxy)benzene and 2,2′-bis(3,4-dicyanophenoxy)-1,3,4-oxadiazole. The resins exhibited a low complex viscosity, with a varying range of processing temperatures for all three systems. Thermogravimetric analysis showed that the synthesized polymers exhibited high thermal and thermo-oxidative stability. The high char yields, which ranged from 64 to 69% at 900 °C under nitrogen atmosphere, and the high glass transition temperatures of the polymers indicated a high crosslinking density in the network structure. Dynamic mechanical measurements demonstrated that the fully cured monomer 2,2′-bis(3,4-dicyanophenoxy)-1,3,4-oxadiazole exhibited no change in glass transition temperature or in storage modulus up to 500 °C.